Proximity sensors have long been used to sense when a device or component is within a predetermined distance of (i.e., in proximity to) a reference location. In many instances, the signals generated by a proximity sensor may be used to selectively enable and disable various portions of a system. For example, if a proximity sensor senses that a device or component is within a predetermined distance of a reference location, this may indicate an undesired configuration. In such an instance, the proximity sensor output signal may be used to disable a system (or portion thereof). Conversely, if a device or component being within a predetermined distance of a reference location is a desired configuration, the proximity sensor output signal may be used to enable a system (or portion thereof).
Proximity sensors have been implemented using various configurations. One particular configuration is generally referred to as the eddy current kill oscillator (ECKO) configuration. With this configuration, the amplitude of a fixed gain oscillator is reduced or eliminated when a device or component is within a predetermined distance of the proximity sensor. The oscillator amplitude is compared to a threshold value, which supplies a binary signal based on this comparison.
One drawback of ECKO proximity sensors is that faulty or erroneous circuit operation can cause false proximity indications. To address this drawback, high-reliability systems may include multiple ECKO proximity sensors so that a faulty or erroneously operating circuit may be detected. This, however, can increase overall system weight and cost. Moreover, adding internal diagnostic circuitry to a proximity sensor can be difficult and costly.
Hence, there is a need for a proximity sensor that includes diagnostic circuitry that may be implemented relatively simply and inexpensively. The present invention addresses at least this need.